Mini Aquariums: The Pros & Cons of Small Fish Tanks

Little fish in fish tank or aquarium, goldfish, guppy and red swortails
pookpiik / Getty Images

The age-old goldfish bowl is getting replaced by safer tiny aquariums in a variety of interesting shapes and sizes. Even the smallest apartment or college dorm room can now be graced with live fish. But are mini aquariums a healthy habitat for the fish? If properly set up and well cared for, yes they can be. But if haphazardly put together and marginally cared for, the fish will be doomed to a very short and unpleasant life.

The Good

The good side of mini aquariums is that anyone can have one. The monetary investment is small, and the space requirements are so minimal that virtually everyone can find a place for a tiny fish tank. College students in dorms, nursing home patients, apartment dwellers, and even the most crowded school classrooms all have space for a mini aquarium. Often apartment building "no pet" rules don't apply to fish. Fish are very relaxing to watch and can provide an opportunity for children to care for a pet in situations where larger pets are not allowed.

The Bad

Like any fish tank, mini aquariums do require maintenance, and they should not be purchased with the notion they can be ignored for long periods. However, the biggest downside of small aquariums is that problems can occur swiftly, and are often fatal before they can be rectified. This is due to the small volume of water in which the fish live, where changes in water chemistry and temperature can happen in a matter of a few hours or, in some cases, just minutes. Therefore it is critical to monitor the water conditions closely and perform water testing and water changes faithfully.

First-time fish owners should be particularly careful during the initial break-in stage of keeping a mini aquarium. Toxins in the water will rise quickly as the biological system is first being established. If water changes are not performed, the levels will become lethal very quickly. Testing is a must, so have water-testing kits on hand or make arrangements with a local pet shop to do the tests for you.

Overcrowding a small aquarium is very easy to do, as we want to put as many fish as possible in the aquarium. Be aware that small aquariums will hold fewer fish per gallon of water than a larger aquarium, by comparison. Overfeeding will pollute a small aquarium with its minimal filtration faster than in larger aquariums, so water quality problems can occur rapidly.

The Ugly

So-called closed systems (i.e., AquaBabies) are becoming widespread in the pet market. The premise is that the system has everything needed to completely sustain itself, with only the occasional feeding of a flake or two of food. For aquarium experts, such a notion is regarded as misleading and disturbing. 

The argument used is that "In nature, there are no food pellets, and the fish must get their nutrients from the environment." While this is true, fish in nature don't live in a few ounces of water devoid of other living things. In nature, fish live in a very large and well-developed ecosystem, where the water supply is massive and is constantly refreshed via rain and moving water currents. That is hardly comparable to a few ounces of water that is rarely if ever changed. And the food supply in a natural environment is not limited to a single plant, supplemented by a few flakes of food every week or two. 

In nature, fish have access to a wide variety of plants, as well as insects, worms, and even other fish. Closed systems contain a plant or two and will either slowly starve to death or succumb to disease caused by the stress of living in such a limited environment.

Systems under one gallon that are advertised as "closed" or "low/no maintenance," should be avoided completely, as they are not healthy for the fish. Examples of these types of systems are:

  • AquaBabies
  • BettaDome
  • Betta in a Vase
  • Do-Little Aquariums
  • Omnarium


Ideally, choose the largest aquarium you have room for. Any system that is so small that it cannot accommodate a filter or heater should be used with great caution. A better option is to look for a small but full-featured aquarium. One of the best is the Eclipse system, which includes a filtration system as well as a built-in light and hood. They are now available in sizes as small as 2 gallons.

Some stores will provide kits in which small aquariums or bowls are sold along with all the necessary items. Keep in mind the needs of the fish you want to keep. If they are not cold-water fish, you'll need an aquarium that can accommodate a heater to keep the temperature in the proper range.

Illustration of the best fish for mini aquariums

The Spruce Pets / Catherine Song

Fish Choices

Fish are cold blooded, which means their body temperature adjusts to whatever the water temperature is. However, fish species vary in the water temperature requirements in which they can survive. Therefore the water temperature required by the fish is a critical factor to consider when making your choices. The other crucial factor is size. Small fish are the only appropriate choice for a mini aquarium. For that reason, goldfish are not a viable choice, as they quickly grow fairly large and produce a lot of waste. Fish that only grow to 1-2 inches as adults are best suited for mini aquariums. Even with these small fish, you may only keep 1-2 fish per gallon of water. A few fish you might consider for a mini aquarium are:

  • Bloodfin tetra: tolerant of cool water, best if kept in a school of three or more fish
  • Guppy: small, and very tolerant of water conditions
  • Platy: very adaptable and usually brightly colored
  • White cloud:  a very hardy fish that prefers cool water
  • Zebra danio: very hardy, they tolerate cooler temperatures fairly well
  • Betta: Great for mini aquariums, but only one per tank; can be mixed with other small fish species. Bettas do not like cool water temperatures, so will require an aquarium heater.